The present invention relates to a method of forming a pattern. More particularly, the present invention relates to a method of forming a pattern using a photosensitive organic polymer.
As the degree of integration for semiconductor devices become higher, the critical dimension (CD) of the pattern formed on a substrate decreases, and at the same time requiring more complex pattern structure. At present, it is difficult to form a photoresist pattern having narrow critical dimension and a dense structure using conventional photolithography techniques.
The art has proposed various methods of forming the photoresist pattern having a desired design. In particular, methods of forming the photoresist pattern using a non-photosensitive organic layer are disclosed in Korean Patent No. 10-396,193 and U.S. Pat. No. 6,670,106 as examples.
FIGS. 1A through 1C are views illustrating processing steps of forming the pattern disclosed in the above-mentioned patents.
Referring to FIG. 1A, a positive photoresist layer is coated on an underlying layer 21 formed on a substrate (not shown), and then a photoresist pattern 22 is exposed and developed to form an opening 25 that exposes the underlying layer 21.
Referring to FIG. 1B, a non-photosensitive organic layer 26 is formed on the photoresist pattern 22 so as to fill the opening 25, and then the non-photosensitive organic layer 26 is etched back using oxygen plasma until a top surface of the photoresist pattern 22 is exposed. Here, the opening 25 has a high step-difference with respect to the photoresist pattern 22 of more than 0.9 μm so that the non-photosensitive organic layer 26 is only slightly formed on the top surface of the photoresist pattern 22 when the non-photosensitive organic layer 26 fills the opening 25.
Referring to FIG. 1C, an entire surface of a resultant structure having the non-photosensitive organic layer 26 and the photoresist pattern 22 is exposed by light such as ultraviolet or X-ray, etc., and then the resultant structure is developed with an alkali-solution to remove the photoresist pattern 22. As a result, the non-photosensitive organic pattern 26a is formed on the underlying layer 21.
According to previously issued patents, if a pattern is formed as the non-photosensitive organic pattern 26a, the pattern may be straight (vertical type). On the other hand, if a pattern such as a photosensitive organic pattern is formed by the positive photoresist layer, the pattern may slope due to diffraction light.
However, as shown in FIG. 2A, when the photoresist pattern 22a having the opening 25a is formed on the underlying layer 21, there is a problem that the width of the opening 25a may decrease as the opening 25a approaches a lower portion of the photoresist pattern 22a. Thus, as shown in FIG. 2B, a contact area 30 between the non-photosensitive organic pattern 26a and the underlying layer 21a is reduced, so that the non-photosensitive organic pattern 26a leans or is separated from the underlying layer 21a during removal of the photoresist pattern 22a with the alkali-solution. These problems occur to such an extent that the critical dimension of the non-photosensitive organic pattern 26a is reduced. In particular, when a film is exposed to light having a short wavelength and high resolution to form a fine pattern, the shorter the wavelength is in the exposure process, the more an allowable limit of a DOF (depth of focus) of the light is reduced. Therefore, if the light of the short wavelength is used in the exposure process, the width of the opening 25a will become incrementally narrower, so that the defocus margin with respect to the DOF is decreased.
It is desirable to form a thin photoresist layer in order to improve the defocus margin. However, the thickness of the non-photosensitive organic pattern 26a is proportional to the thickness of a photoresist layer for forming the photoresist pattern 22a. As a result, while the underlying layer 21a is etched, a lower portion of the underlying layer 21a is also etched because the non-photosensitive organic pattern 26a is insufficient to serve as an etching mask.